Did you notice the "dings" in the wooden braces in the tunnel closest to Santa Cruz (right before the street running). Presumably they are still there. From what I was told when I was working for SP in that area, that is an original SPC ng. tunnel that never got enlarged when the line was standard gauged. The modern standard gauge cars didn't fit very well, and more than one brace paid the price. I was told that on some occasions the springs were removed from cars in order to get them through the tunnel. I believe the other tunnels on the line were enlarged.